1. Field of the Invention
The present invention relates to a technique of improving deterioration of a captured image caused by hand shake during image captured by an optical apparatus such as a digital camera. In particular, the present invention relates to a technique of reducing image blurring caused, for example, by hand movement in the optical-axis direction during macro image-capturing.
2. Description of the Related Art
An optical apparatus such as a camera or an interchangeable lens is often provided with an image stabilizer that improves an image blur caused by hand-induced shake or the like.
The hand-induced shake is a vibration normally having a frequency ranging from 1 to 10 Hz. The image stabilizer mainly corrects image blurring caused by vibrations having such a frequency. For image stabilization, the vibration of the optical apparatus is detected. Then, a technique like optical image-stabilization or electronic image-stabilization is used. Optical image-stabilization shifts a correction lens in a plane orthogonal to the optical axis in accordance with the detected vibration. The electronic image-stabilization varies an area, from which data is output as an image, from within the total pixel area of the imaging element.
If the image-capturing magnification is 0.1 or lower, in general, image blurring can be reliably corrected only by correcting an angular blur in a direction in which the image pickup surface tilts. If the image-capturing magnification is higher than 0.1, the effect of blurring in a parallel direction, i.e., in vertical and horizontal directions (hereinafter, referred to as a shift blur), and the effect of blurring in the optical-axis direction (hereinafter, referred to as a focus blur) may increase. FIG. 1 is a graph showing the effects of the blurs. FIG. 1 plots image-capturing magnification in the x direction and displacement of the image in an image plane due to blurring in the y direction.
To improve (i.e. reduce) the blurs in an optical apparatus having a high image-capturing magnification such as a macro lens, a technique has been proposed that detects a shift blur and a focus blur with an acceleration sensor or the like, and drives and controls a correction system on the basis of the detection output (see Japanese Patent Laid-Open No. 09-080523).
The above-mentioned electronic image-stabilization is frequently used in apparatus for recording movies, such as a video camera.
In the field of still images, a technique has been proposed in which a plurality of underexposure images are captured at a shutter speed which is hardly affected by hand shake, positional shifts among the images are then corrected, and the images are combined, so as to reduce the blurring and obtain a still image with an optimum exposure (see Japanese Patent No. 03110797).
With the above technique, since the positional shifts among the images can be acquired using the captured images, a blur detection element such as a vibrating gyroscope is not necessary. Also, since the correction is performed on the basis of a blur signal from the image pickup surface, the above-mentioned shift blur and angular blur do not have to be considered separately.
With both techniques described above, the angular blur and shift blur can be reliably corrected.
However, with the technique of Japanese Patent Laid-Open No. 09-080523, the focus lens is moved in an optical-axis direction to correct the focus blur, causing the following problems.
First, as the focus lens is moved in the optical-axis direction, the angle of field is changed. This is one of the important factors of the deterioration in images when high magnification image-capture such as macro image-capture is performed. If a lens for correcting the angle of field is additionally provided for preventing the deterioration in images, the correction system may become complicated. Further, an existing focus lens driving system for auto-focusing cannot accurately follow the blur because the driving characteristic of a motor is insufficient and the backlash is large. While the technique of Japanese Patent No. 03110797 is effective for a shift blur, the patent does not disclose nor suggest correction of a focus blur.